Engineering thermoplastics are used extensively in many components of aircraft interiors, such as wall panels, overhead storage lockers, serving trays, seat backs, cabin partitions, and ducts. Engineering thermoplastics are economically fabricated into these components by extrusion, thermoforming, injection molding, and blow-molding techniques.
United States Government standards for the flame resistance of construction materials used for aircraft interiors are set out in the 1986 amendments to Part 25-Airworthiness Standards--Transport Category Airplanes of Title 14, Code of Federal Regulations (see 51 Federal Register 26206, July 21, 1986 and 51 Federal Register 28322, Aug. 7, 1986). The flammability standards are based on heat calorimetry tests developed at Ohio State University (hereinafter "OSU Tests") Such OSU Tests are described in the above-cited amendments to 14 CFR Part 25 and are incorporated herein by reference. These tests measure the two minute total heat release (in kilowatts minute per square meter of surface area, KW.min/m.sup.2) as well as the maximum heat release rate (in kilowatts per square meter of surface area, KW/m.sup.2) over the first five minutes for the material being tested, when burned under a specified set of conditions. The 1986 standards required engineering thermoplastics to have both of these heat release measurements under 100. The new 1990 compliance standards will allow a maximum of 65 for each of the two heat release measurements. Hence, a need exists to develop new thermoplastic compositions that will be able to meet these flammability standards, and yet display at the same time such other desirable features as toughness, chemical, solvent and cleaner resistance, and ease of fabrication into finished components.
Flame retarding additives such as triphenyl phosphate or aluminum trihydrate which generally possess low flammability have been mixed with engineering thermoplastics to reduce flammability of the thermoplastics. However, a blend of such a low flammability additive with high performance engineering thermoplastics often does not yield a useable flame-resistant composition. For example, the low flammability additive may not be compatible, i.e. miscible with the engineering thermoplastic, at additive concentrations necessary to achieve significant flame retardance, or the additive may not be stable at the processing temperatures of the engineering thermoplastic. Furthermore, low flammability additives which are compatible with a particular engineering thermoplastic often cannot effectively lower the flammability or heat release of the thermoplastic. If the effect on flammability is merely a reduction due to dilution, amounts of the low-flammability additive necessary to achieve a desired reduction in flammability can adversely affect the physical properties or processibility of the engineering thermoplastic.
Thermoplastic blends consisting of a poly(aryl ether sulfone) and a poly(aryl ether ketone), containing a filler and/or a reinforcing fiber, are known; see Saito et al., U.S. Pat. No. 4,804,697 and Itteman et al., European Patent Application No. 297,363. Phase behavior of such blends was studied by Wu et al., Angew. Makromol. Chem. 171, 119-130 (1989). Mixtures of poly(aryl ether sulfones), which contain biphenyl groups, with poly(aryl ether ketones) are disclosed in European Patent Application No. 254,455 and in Harris et al., U.S. Pat. Nos. 4,713,426 and 4,804,724. These disclosures do not address improvement of the flammability of blends of poly(aryl ether sulfones) with poly(aryl ether ketones).
Blends of fluorocarbon polymers with either a poly(aryl ether sulfone) or a poly(aryl ether ketone) are disclosed in Vary, U.S. Pat. No. 3,992,347; Attwood, U.S. Pat. No. 4,131,711; Vasta, U.S. Pat. No. 4,169,117; and Saito et al., U.S. Pat. No. 4,578,427. These disclosures are not directed to flame retardant blends of a poly(aryl ether ketone) and a poly(aryl ether sulfone). Mixtures of polyarylene polyethers with 0.1 to 30.0 weight percent vinylidene fluoride-hexafluoropropene copolymer were described by Barth, U.S. Pat. No. 3,400,065. Several types of poly(aryl ether sulfone) are disclosed as examples of the polyarylene polyethers used in Barth's mixture. Barth does not disclose flame retardant blends of a poly(aryl ether ketone) and poly(aryl ether sulfone). Mixtures containing a fluorocarbon polymer, e.g., polytetrafluoroethylene, perfluorinated poly(ethylene-propylene) copolymer, or poly(vinylidene fluoride), with a number of engineering polymers including poly(aryl ether sulfones), are disclosed in European Patent Application No. 106,764. Blends of poly(aryl ether ketones) with non-crystalline copolymers of tetrafluoroethylene are disclosed in Petersen, U.S. Pat. No. 4,777,214. Composite materials consisting of a mixture of poly(aryl ether sulfone), a fluorocarbon polymer, and carbon fibers or of a mixture of poly(aryl ether ketone), a fluorocarbon polymer, and potassium titanate fibers are disclosed as useful for moldings in Japanese Patents 88/065,227B and 89/029,379B). None of these references disclose poly(biphenylene ether sulfone compositions comprising zinc borate.
Rock et al., European Patent Application No. 307,670, describes mixtures of 10 weight percent of a perfluorocarbon polymer with each of a polysulfone or a polyether sulfone or a polyether ketone as having improved heat release characteristics. Rock also describes the use of the perfluorocarbon polymer, finely divided titanium dioxide or mixtures of perfluorocarbons and titanium dioxide to improve the flammability characteristics of blends of a polyetherimide with a polyetherimide-siloxane block copolymer. Rock ascribes the beneficial effect of the titanium dioxide on flame retardency of these polyetherimide blends to interaction between the TiO.sub.2 and the siloxane moiety of the block copolymer portion of the blend. Rock does not disclose flame retardant poly(biphenyl) ether sulfones) or flame retardant blends of a poly(biphenyl ether sulfone) with a poly(aryl ether ketone) or a poly(aryl ether sulfone).
U S. Patent Application, Ser. No. 07/504,779, filed Apr. 4, 1990, entitled "Flame Resistant Thermoplastic Compositions" is commonly assigned to Amoco Corporation. That application is directed to thermoplastic materials which comprise a poly(biphenyl ether sulfone), a fluorocarbon polymer and titanium dioxide. These materials are disclosed as optionally including a poly(aryl ether ketone) or a poly(aryl ether sulfone). The materials of the commonly assigned application exhibit improved heat release values.
Zinc borate has been used in various thermoplastic compositions. Cella, et al., U.S. Pat. No. 4,833,190 discloses use of hydrated zinc borate as a smoke suppressant and flame retardant in silicone containing compositions Anderson, U.S. Pat. No. 4,049,619 discloses a thermoplastic composition of a polysulfone, a flame retarding bis-phenoxy compound and an enhancing agent for the bis-phenoxy compound, which is disclosed as one of numerous metal oxides or other materials. Zinc borate is listed as one possible enhancing agent. Neither Anderson nor Cella discloses flame retardant poly(biphenyl ether sulfones) or flame retardant blends of a poly(biphenyl ether sulfone) with a poly (aryl ether ketone) or a poly(aryl ether sulfone).
Presently, three polysulfone engineering thermoplastics are commercially available: polysulfone, such as UDEL.RTM. from Amoco Performance Products, Inc.; poly(aryl ether sulfones) which do not contain biphenyl groups, such as VICTREX.RTM. from Imperial Chemical Industries; and poly(biphenyl ether sulfones), such as RADEL.RTM. R from Amoco Performance Products, Inc. Of these, poly(biphenyl ether sulfones) are the most expensive due to the high cost of biphenol used to produce the polymer. However, the poly(biphenyl ether sulfones) have the highest use temperature of these three and exhibit enhanced compatibility with poly(aryl ether ketones) as disclosed in Harris, U.S. Pat. Nos. 4,713,426 and 4,804,724.
It is the general object of the invention to provide thermoplastic compositions having improved heat release properties, particularly compositions based on poly(biphenyl ether sulfones). It is a specific object to provide thermoplastic compositions having improved flammability performance in aircraft interior parts, including improved resistance to flammability according to the OSU Test. It is another specific object to provide such compositions which are readily processable in both injection molding and sheet extrusion. It is another specific object to provide such compositions having excellent chemical and solvent resistance. Other objects will appear below.
It was unexpectedly discovered that the objects of the invention could be attained by compositions comprising a polyarylether comprising at least one poly(biphenyl ether sulfone) and zinc borate. The compositions can also contain other polyarylethers, including such compositions which further comprise a poly(aryl ether ketone) or a poly(aryl ether sulfone) or additives such as a fluorocarbon polymer and/or titanium dioxide. The compositions of the invention display an unexpected combination of excellent mechanical properties, superior chemical resistance, and very low flammability. Moreover, they are easy to melt-fabricate and yield molded articles having smooth and aesthetically pleasing surface characteristics. The instant compositions are useful in a number of applications, in particular for the construction of various panels and parts for aircraft interiors. None of the above references disclose or suggest a combination of a poly(biphenyl ether sulfone) and zinc borate.